1. Field of the Invention
The present invention relates to an electrophotographic photoconductor comprising an electroconductive support end a photoconductive layer formed thereon, which comprises a diamine compound as a photoconductive material.
2. Discussion of Background
Conventionally, inorganic materials such as selenium, cadmium sulfide end zinc oxide are used as photoconductive materials of an electrophotographic photoconductor in an electrophotographic process.
The electrophotographic process is one of the image formation processes, through which the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity, for instance, by corona charging. The uniformly charged photoconductor is exposed to a light image to selectively dissipate the electric charges of the exposed areas, so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed into a visible toner image by a toner or developer comprising a coloring agent such as a dye or pigment, and a binder agent such as a polymeric material.
Fundamental characteristics required for the photoconductor in such an electrophotographic process are: (1) chargeability to an appropriate potential in the dark, (2) minimum dissipation of electrical charges in the dark, and (3) rapid dissipation of electrical charges when exposed to light.
However, while the above-mentioned inorganic materials have many advantages, they have several shortcomings from the viewpoint of practical use.
For instance, a selenium photoconductor, which is widely used as present, satisfies the above-mentioned requirements (1) to (3) completely, but it has the shortcomings that the manufacturing conditions are difficult and, accordingly, its production cost is high. In addition, it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to heat and mechanical shocks that it must be handled with the utmost care.
A cadmium sulfide photoconductor and a zinc oxide photoconductor can be easily obtained by dispersing cadmium sulfide particles and zinc oxide particles respectively in a binder resin, and coating the thus prepared coating liquid on a support. However, they are poor in mechanical properties, such as surface smoothness, hardness, tensile strength and wear resistance. Therefore, they cannot be used repeated as they are.
To solve the problems of the inorganic materials, various electrophotographic photoconductors employing organic materials have recently been proposed and some are already used practically. For example, there are known a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on, as disclosed in U.S. Pat. No. 3,484,237; a photoconductor prepared by sensitizing poly-N-vinylcarbazole with a pigment of pyrylium salt, as disclosed in Japanese Patent Publication 48-25658; a photoconductor comprising as the main component an organic pigment as disclosed in Japanese Laid-Open Patent Application 47-37543; a photoconductor comprising as the main component a eutectic crystal complex of a dye and a resin, as disclosed in Japanese Laid-Open Patent Application 47-10735; a photoconductor prepared by sensitizing a triphenylamine compound with a sensitizer pigment, as disclosed in U.S. Pat. No. 3,180,730; a photoconductor comprising an amine derivative as a charge transporting material, as disclosed in Japanese Laid-Open Patent Application 57-195254; a photoconductor comprising poly-N-vinylcarbazole and an amine derivative as charge transporting materials, as disclosed in Japanese Laid-Open Patent Application 58-1155; and a photoconductor comprising as a photoconductive material a polyfunctional tertiary amine compound, in particular, a benzidine compound, as disclosed in U.S. Pat. No. 3,265,496, Japanese Patent Publication 39-11546 and Japanese Laid-Open Patent Application 53-27033.
These electrophotographic photoconductors have their own excellent characteristics and considered to be valuable for use in practice. With various requirements of the electrophotographic photoconductor in the electrophotographic process taken into consideration, however, the above-mentioned conventional electrophotographic photoconductors cannot always meet all of the above-mentioned requirements.
Electrophotographic photoconductors which comprise carbonate-group-containing compounds as the photoconductive materials are disclosed in U.S. Pat. Nos. 4,801,517, 4,806,443 and 4,806,444, and Japanese Laid-Open Patent Applications Nos. 3-221522 and 4-11627. Each of the carbonate-group-containing compounds for use in the photoconductors is a polymeric compound, so that it is difficult to purify the carbonate-group-containing compound by column chromatography, recrystallization, distillation or sublimation in order to obtain such a high purity as required for the photoconductive material. Therefore, impurities cannot completely be removed from the above-mentioned photoconductors, so that not all the requirements for the photoconductor can be satisfied.
There is widely used an electrophotographic photoconductor of which photoconductive layer is prepared in such a manner that a low-molecular photoconductive material is dissolved or dispersed in a binder resin solution to form a resin composition and the photoconductive layer is formed by casting the above prepared resin composition. However, when the photoconductive layer is formed by using a mixture of the low-molecular photoconductive material and the binder resin, as mentioned, the resin solution of the photoconductive material easily tends to cause gelation to become white opaque, and induces phase separation depending on the kind of binder resin employed. As a result, a uniform photoconductive layer cannot be obtained, which has an adverse effect on the electrostatic properties and the durability of the photoconductor.
Furthermore, as described in Japanese Laid-Open Patent Application 3-221522, there are the problems of the gelation of a photoconductive layer coating liquid, and partial crystallization and cracks of the obtained photoconductive layer when a single high-molecular photoconductive material is used to prepare a coating liquid for the photoconductive layer. According to the description in the aforementioned application, it is required that the copolymerization ratio of the high-molecular photoconductive material be controlled and the viscosity of the coating liquid for the photoconductive layer be adjusted to solve the above-mentioned problems.